JP-A-2002-361931 discloses an image forming apparatus exposing a photosensitive drum by the use of an LED head, in which a spacer maintaining a gap (hereinafter, also referred to as “operating distance”) in an optical axis direction between the LED head and the photosensitive drum is disposed between the LED head and the photosensitive drum. In the image forming apparatus, an eccentric cam is disposed between the plate-like spacer and the LED head and the gap in the optical axis direction between the spacer and the LED head, that is, the operating distance, can be minutely adjusted by the use of the eccentric cam.
Since the operating distance is very small, the size of the eccentric cam or the spacer should be very small, thereby limiting the precision of adjustment using the eccentric cam or the stroke. When such limitation exists, it is possible to precisely set the operating distance, thereby deteriorating image quality.
Further, since the LED head is pressed to a photosensitive drum with the eccentric cam and the spacer interposed therebetween, a stress may be applied to the LED head itself and the LED head may be deformed. When the rigidity is enhanced by manufacturing the LED head out of aluminum die-cast to resist the deformation, the LED head increases in size, thereby increasing the cost thereof.